It is known from practice that both emission control devices such as catalytic converters or exhaust gas scrubbers and silencers can be arranged downstream of an internal combustion engine as exhaust-gas aftertreatment modules. The catalytic converters are used in particular for nitrogen removal and/or desulphurization of the exhaust gas and therefore the reduction of nitrogen-oxide emissions and sulphur-oxide emissions. The silencers are used for noise reduction and thus reducing sound emissions.
Silencers known from practice are typically positioned downstream of an emission control device and realized as what are known as resonance or lambda/4 silencers, which are based on the fact that chambers of the silencers have a depth or length adapted to the frequency of the exhaust noise to be damped. Silencers of this type have a narrow-banded damping action however, so that in particular in the case of engines which are operated with variable speed and therefore have different exhaust frequencies, it is not possible to realize a satisfactory exhaust sound damping.
In order to provide silencers with wide-banded damping action for exhaust sound damping, it is known from the prior art to equip silencers with a plurality of chambers, which are released via valves, as a result of which the depth of the chambers can be adapted to the frequency of the exhaust sound to be damped.
Silencers of this type have the disadvantage however, that movable parts are located in the exhaust-gas flow, which have a strong tendency to corrosion in particular if the internal combustion engine, the exhaust sound of which is to be damped, is operated using high-sulphur fuels. Furthermore, in silencers of this type, only a plurality of narrow-banded frequency ranges can be subjected to an effective sound damping, an infinitely variable adaptation of the damping action of the silencer to different frequency ranges of the exhaust sound to be damped is not possible.
DE 196 11 133 A1 and DE 196 19 173 C1 in each case disclose silencers with movable parts exposed to the exhaust-gas flow.
On this basis, it is one object of the present invention to create a novel exhaust-gas aftertreatment device and method for exhaust-gas aftertreatment.